An attempt to determine the way in which furosemide is absorbed, distributed, metabolized, and excreted as well as the way it effects the whole living system when infused intravenously into healthy elderly and young subjects. Furosemide is a potent diuretic, which is used in the treatment of swelling associated with congestive heart failure, cirrhosis of the liver, and kidney disease. It can also be used to control high blood pressure in adults. This study will try to develop a model that incorporates physiologic variables to account for observed differences in the way the body reacts in the population of young and elderly healthy people. Since furosemide has been used, it may increase urine output with the first dose, but not as much with later doses. This is referred to as tolerance and this study will try to determine why this happens. The study will use six healthy young subjects and six healthy elderly subjects to see if there are any differences between the groups when each is given a dose of furosemide. Each subject will be tested two times, at least one week apart. Initially, a history, physical exam, ECG and laboratory studies will be done to determine eligibility. There will be a fixed diet with certain foods and salt for two days before the admission to the study unit. On the first day, the subjects will be required to lie in bed for 12 hours except for meals and trips to the bathroom. On the next day, the same procedure is used, plus the infusion of a medication to measure the function of the kidneys. The study drug will also be infused. During this time, as the drug is increasing the flow of urine, it will be collected every 30 minutes for four hours and then every six hours. Blood will be taken. The second visit will be the same except that the amount of urine output will be replaced in the form of a salt solution through the mouth or intravenously. After the study, there will be another physical exam, ECG, and laboratory evaluation performed.